The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An electric quarter sheet sander is a type of orbital sander having an electric motor that drives an orbit mechanism that moves a platen in an orbital pattern. A sheet of sandpaper is removably fastened to the platen. When the platen with the sandpaper fastened thereto is applied to a work surface, such as to wood, the orbital motion of the platen moves the sandpaper in an orbital motion against the work surface to sand it. Since a full sheet of sandpaper is 9″×11″ and the sheet of sandpaper fastened to the platen is 4 ½″×5 ½″, or ¼ of a full sheet of sandpaper, sanders of this type are commonly known as ¼ sheet sanders.
One disadvantage ¼ sheet electric sanders have suffered is due to the height of the sander. If the user grasps the sander by placing the palm of the user's hand over the top of the sander, the user's hand is sufficiently far from the work that the user is sanding to cause more fatigue than is the case with pneumatic orbital or random orbital sanders where the user can grasp the sander close to the work piece. This often leads to user's grasping electric ¼ sheet sanders on the side of the sander. This tends to be awkward compared to grasping the top of the housing. Also, the greater height of the ¼ sheet electric sander causes more wobble compared to the lower height pneumatic orbital sander.
FIGS. 1, 3, 5 and 7 show a prior art Black & Decker QS800 series and KA171 ¼ sheet electric sander 100. Sander 100 has a housing 102 that includes first and second clamshell halves 104, 106 mated together. An upper portion of housing 102 is formed as a handle 108. An on-off switch 110 is disposed in front end 109 of handle 108 of housing 102. An electric motor 300 (FIGS. 3 and 5) is disposed in housing 102. Electric motor 300 is a universal AC motor having a field or stator 302 and an armature 308. Stator 302 includes a lamination stack 304 having field coils 306 wound in slots (not shown) therein. Motor 300 is a two-pole motor and stator 302 includes two field coils 306. Armature 308 extends through lamination stack 304 of stator 302. Armature 308 has an armature shaft 310 extending through and affixed to a lamination stack 312. Lamination stack 312 includes slots (not shown) in which armature coils (not shown) are wound. Portions of armature shaft 310 generally at upper end 316 and lower end 318 (FIG. 7) thereof (as oriented in the drawings) are entrained in upper bearing 320 and lower bearing 322 (FIG. 7) (as oriented in the drawings). Upper and lower bearings 320, 322 are received in bearing holders 324, 326 formed in clamshell halves 104,106 of housing 102. A commutator 314 is affixed to armature shaft 310 toward upper end 316 thereof.
A fan 328 is affixed to armature shaft 310 toward a lower end of armature shaft 310 and an orbit mechanism 330 (FIG. 5) is coupled to the lower end 318 of armature shaft 310. Fan 328 is illustratively disposed in housing 102 and at least a portion of orbit mechanism 330 (FIG. 5) extends below a bottom 111 of housing 102. A platen 112 is coupled to orbit mechanism 330. A ¼ sheet of sandpaper 114 is removably secured to platen 112.
Clamshell housing halves 104, 106 each include a plurality of screw bosses, illustratively six, for receiving screws (not shown) that hold clamshell halves 104, 106 together. The screw bosses may illustratively be threaded screw bosses in one of clamshell halves 104, 106 and through holes in the other of clamshell halves 104, 106. The screw bosses of each clamshell housing half include a pair of upper screw bosses 336 generally at opposite sides of upper bearing 320, a pair of lower screw bosses 338 generally at and slightly above opposite sides of lower bearing 322, and a pair of screw bosses 340 (FIG. 5) at an upper back end of handle 108 of housing 102 generally where a cordset 116 enters housing 102 and connects to a terminal block 341 (FIG. 3). When clamshell halves 104, 106 are mated together, the screw bosses extend across housing 102 from one clamshell half 104 to the other clamshell half 106. Switch 110 and terminal block 341 are disposed in a horizontal elevation (when sander 100 is upright) above a horizontal elevation of brush boxes 332.
Two brush boxes 332 are disposed on opposite sides of commutator 314 in respective brush box retainers 334 formed in clamshell halves 104, 106 of housing 102. Brush boxes 332 are located in housing 102 so that they bridge across clamshell halves 104, 106 of housing 102. Stator 302 of electric motor 300 is located in housing 102 so that one field coil 306 is disposed in clamshell half 104 and the other field coil 306 is disposed in clamshell half 106 and are generally parallel to each other. Each field coil 306 thus extends across the respective clamshell half 104, 106 in which it lies and not toward the other clamshell half 104, 106. When clamshell halves 104, 106 are mated, edge 344 of clamshell half 104 and edge 346 (FIG. 5) of clamshell half define a vertical plane 352 (when sander 100 is upright). A horizontal (when sander 100 is upright) centerline 348 (FIG. 7) of brush boxes 332 (a line that extends through the centers of the brush boxes 332) lies in that vertical plane 352 and a horizontal centerline 350 (FIG. 7) of field coils 306 (a line that extends through the centers of field coils 306) lies in a vertical plane 354 that is rotated ninety degrees with respect to plane 352. Centerline 348 (FIG. 7) of brush boxes 332 and centerline 350 (FIG. 7) of field coils 306 are thus rotated ninety degrees with respect to each other.
As best shown in FIG. 5, field coils 306 are sufficiently wide so that they bridge across lower screw bosses 338 and housing 102 must thus have sufficient height so that lower ends 342 of field coils 306 are above lower screw bosses 338. As best shown in FIG. 3, switch 110 and terminal block 341 are disposed above brush boxes 332.
Sander 100 has a height, the distance from the top of handle 108 to the bottom of platen 112, of 155 mm. Lamination stack 304 of stator 302 of electric motor 300 has a height of 25 mm and commutator 314 has a height of 15 mm. Electric motor 300 is illustratively a 230 volt, 50 Hz, 200 watt, 15,000 RPM (no load speed) motor or a 120 volt, 60 Hz, 2 amp, 15,000 RPM (no load speed) motor.